In gas turbines, the air-liquid fuel mixture is fed to the turbine combustion chamber by a fuel injection, air-fuel mixing assembly comprising a perforated combustion-supporting air inlet portion; end fuel feed pipes; and a conical tubular body, which is housed inside the perforated portion, tapers towards the combustion chamber, and has an axis extending through the combustion chamber. The conical tubular body separates two air-liquid fuel mixing conduits: an inner conduit, into which the liquid fuel is sprayed by a ring of nozzles; and an outer annular conduit, into which the liquid fuel is fed by a further ring of nozzles at a distance from the outer surface of the conical tubular body and oriented to feed the liquid fuel towards an outer wall of the annular conduit.
Before reaching the combustion chamber, the air and fuel must be mixed thoroughly, using the turbulence generated by the air.
Tests show that the location and orientation of the further ring of nozzles cannot be relied on to produce the desired mixture in all operating conditions of the combustor, and that the mixture varies according to the quantity and characteristics (e.g. density) of the airflow along the conduits. As a result, the air-liquid fuel mixture fed to the combustion chamber is not always homogeneous, by varying from one part of the conduit to another, thus resulting in the formation of fumes and large amounts of contaminating combustion products in general.
One solution comprising walls for guiding the liquid fuel in a direction substantially parallel to a generating line of the outer surface of the conical tubular portion is described, for example, in Patent Application WO2010/037627, in which the walls are housed inside the conduit into which the liquid fuel and combustion-supporting air are fed. Solutions of this sort, however, are relatively complex in design.